Are there any sources of film which is only sensitive to blue light?
I like to experiment and I wanted to illustrate the way black & white film has developed from blue-ortho 7 then panchromatic film.

Have you checked out Ilford Ortho Plus? It's supposed to be a continuous tone ortho film.

Kodak commerical internegative film? But it's been killed by Kodak. You might find some in a store fridge. Maybe somebody makes a graphic film?

http://www.kodak.com/global/en/professional/support/techPubs/f16/f16.jhtml

I don't think it was cheap.

While not perfect it might be easier to just use a deep blue filter. A #47 filter should pass nothing but blue light.

Isn't this why the old-time guys used to sandwich-print their landscape work with a cloudy-sky + primary-subject neg? Otherwise, blue-sensitive film would show a stark white sky in a positive print.